Using local helioseismology, we construct maps of the horizontal divergence of the velocity field near the solar surface and study the spectrum of solar supergranulation during the period from 1996 to 2002. Supergranulation oscillates and propagates like a wave interference pattern. The variations of the oscillation frequency with latitude and time are less than 5%. We find significant solar-cycle variations in the lifetime and the anisotropic distribution of power. We also measure the time-dependent zonal and meridional flows that advect supergranules.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html